Good morning formin72.

You have rarely seen them called out because....they are rarely called out.    There is no requirement that they be called out for every weld.  Even less reason to prescribe the method than to specify finishing at all.  And there is seldom, when considering all welding done in any given day, a need for the majority of welds to have any type of finishing done to the surface of the weld.  But even when they are deemed necessary the engineer will most usually leave the method to the contractor's discretion. 

Most welds are never going to be seen anyway and it is more about cosmetics than it is about stress risers or any true structural application.  Especially with welders who can earn their salt and put down weld that is reasonably smooth.  Occasionally it will be to accommodate a second fit and the weld can't be in the way. 

Grinding is probably the most chosen method but it all depends upon the purpose or application of the member and the reason then for needing any kind of finishing.

He Is In Control, Have a Great Day,  Brent